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CERT(*) Advisory CA-95:07a
Original issue date: April 21, 1995
Last revised: September 23, 1997
Update copyrigth statement
A complete revision history is at the end of this file.
Topic: SATAN Vulnerability: Password Disclosure
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*** This is a revised CERT advisory.***
It addresses inaccurate information in CA-95:07
and contains information about SATAN 1.1.1.
*** Supersedes CA-95:07 ***
There was a potential vulnerability introduced into systems running SATAN 1.0
and earlier, as described below. The problem has been addressed in version 1.1
and later. The CERT/CC team recommends that you take the precautions described
in Section III below before you run SATAN and that you upgrade to the latest
version of SATAN--currently 1.1.1.
The following two statements from CA-95:07 are inaccurate.
1. This statement is incorrect: "Note that SATAN 1.1 is expected to check
systems for this SATAN 1.0 vulnerability as part of scanning other
systems."
2. This statement is misleading: "This vulnerability affects all systems
that support the use of SATAN with the HTML interface." For SATAN 1.0
and earlier, whether a system is vulnerable depends on the system
configuration, the net browser supporting SATAN, and how SATAN is used.
The problem has been solved in later versions of SATAN.
We will update this advisory as we receive additional information.
Please check advisory files regularly for updates that relate to your site.
For an overview of a beta version of SATAN, see CERT advisory CA-95:06.
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I. Description
In SATAN version 1.0, access to the SATAN processes is protected by a
session key (also referred to as a "magic cookie" or "password"). SATAN
itself never sends this session key over the network. However, depending
on the configuration at your site, the supporting HTML browser, and how
you use SATAN, your session key may be disclosed through the network.
Local or remote users who obtain your session key can run perl scripts
that are on the system running SATAN.
If you use SATAN only through the command line interface, your system is
not vulnerable to the problem because there is no session key.
Additional details are in the "SATAN Password Disclosure" tutorial
provided with SATAN. We have included the tutorial as an Appendix B of
this advisory.
II. Impact
If the session key is disclosed while SATAN 1.0 is running, unauthorized
local or remote users can execute perl scripts as the user of the process
running SATAN (typically root).
III. Solution
1. Obtain and install SATAN version 1.1.1, which addresses the problem.
For details on how the problem is addressed, see the section entitled
"Additional SATAN Defenses" in the SATAN Password Disclosure tutorial.
The SATAN authors also provide guidance on protecting access; see the
tutorial section, "Preventing SATAN Password Disclosure."
SATAN 1.1.1 is available from many sites, including
ftp://ftp.win.tue.nl/pub/security/satan-1.1.1.tar.Z
ftp://ftp.win.tue.nl/pub/security/satan-1.1.1.README
ftp://ftp.win.tue.nl/pub/security/satan-1.1.1.tar.Z.asc
MD5 (satan-1.1.1.tar.Z) = de2d3d38196ba6638b5d7f37ca8c54d7
MD5 (satan-1.1.1.README) = 3f935e595ab85ee28b327237f1d55287
MD5 (satan-1.1.1.tar.Z.asc) = a9261070885560ec11e6cc1fe0622243
To locate other sites, you can send mail to
majordomo@wzv.win.tue.nl
and put in the body of the message (not the subject line):
get satan mirror-sites
There are reports of modified copies of SATAN, so ensure that the copy
that you obtain is authentic by checking the MD5 checksum or SATAN
author Wietse Venema's PGP signature. Appendix A of this advisory
contains his PGP key.
We urge you to read the SATAN documentation carefully before
running SATAN.
2. We also recommend that you take the following precautions:
* Install all relevant security patches for the system on which you
will run SATAN.
* Execute SATAN only from the console of the system on which it is
installed (e.g., do not run SATAN from an X terminal, from a
diskless workstation, or from a remote host).
* Ensure that the SATAN directory tree is not NFS-mounted (or AFS,
etc.) from a remote system.
* Ensure that the SATAN directory tree cannot be read by users other
than root.
* Do not open any URLs outside your own system and site while
running the browser started by SATAN. For example, do not use
previously stored URLs such as those found in bookmarks and
pull-down menus.
* Do not link to any URLs outside your own system and site while
running the browser started by SATAN. If you use external links
while SATAN is running from the SATAN browser, security can be
compromised on the system from which you are executing SATAN. So,
for example, do not use previously stored links such as those found
in bookmarks and pull-down menus.
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Appendix A: Wietse Venema's PGP Key
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Appendix B: Tutorial - SATAN Password Disclosure
The following tutorial can be found in
satan-1.1.1/html/tutorials/vulnerability/SATAN_password_disclosure.html
SATAN Password Disclosure
SUMMARY
SATAN password disclosure via flawed HTML clients or environmental
problems
IMPACT
Unauthorized users may execute commands through SATAN
BACKGROUND
By default, SATAN runs as a custom HTML (hypertext markup language)
server, executing requests from a user-provided HTML browser, or
client program. Examples of common HTML clients are Netscape, NCSA
Mosaic and Lynx.
An HTML client request is nothing but a network message, and
network messages may be sent by any user on the network. To defend
itself against requests from unauthorized users, SATAN takes the
following precautions:
* SATAN generates a session key, to be used as a secret password,
each time it starts up an HTML client. The session key is in the
form of a 32-byte quasi-random number. The number is called
quasi-random because it is impossible to generate real random
numbers using only software.
* SATAN creates HTML files with the secret password embedded in URL
(uniform resource locator) links. The HTML file access
permissions are restricted to the owner of the SATAN process (and
the superuser).
* SATAN rejects HTML requests whose URL does not contain the
current SATAN password. This requirement prevents access by
unauthorized clients, provided that the current SATAN password is
kept secret.
The protection scheme used by SATAN is in essence the same as the
scheme used by many implementations of the X Window system: MIT
magic cookies. These secrets are normally kept in the user's home
directory, in a file called .Xauthority. Before it is granted
access to the screen, keyboard and mouse, an X client program needs
to prove that it is authorized, by handing over the correct magic
cookie. This requirement prevents unauthorized access, provided
that the magic cookie information is kept secret.
THE PROBLEM
It is important that the current SATAN password is kept secret.
When the password leaks out, unauthorized users can send commands
to the SATAN HTML server where the commands will be executed with
the privileges of the SATAN process.
Note that SATAN generates a new password every time you start it up
under an HTML client, so if you are suspicious, simply restart the
program.
SATAN never sends its current password over the network. However,
the password, or parts of it, may be disclosed due to flaws in
HTML clients or due to weak protection of the environment that
SATAN is running in. One possible scenario for disclosure is:
* When the user selects other HTML servers from within a SATAN
session, some HTML client programs (Netscape and Lynx) disclose
the current SATAN URL, including SATAN password information. The
intention of this feature is to help service providers find out
the structure of the world-wide web. However, the feature can
also reveal confidential information. With version 1.1 and later,
SATAN displays a warning when the HTML client program exhibits
this questionable (i.e. stupid) feature.
Other scenarios for SATAN password disclosure are discussed in the
next section, as part of a list of counter measures.
PREVENTING SATAN PASSWORD DISCLOSURE
The security of SATAN is highly dependent on the security of
environment that it runs in. In the case of an X Window
environment:
* Avoid using the xhost mechanism, but use xauth and MIT magic
cookies or better. Otherwise, unauthorized users can see and
manipulate everything that happens with the screen, keyboard and
mouse. Of course, this can also be a problem when you are not
running the SATAN program at all.
Steps that can help to keep the X magic cookie information secret:
* Avoid sharing your home directory, including .Xauthority file,
with other hosts. Otherwise, X magic cookie information may be
captured from the network while the X software accesses that
file, so that unauthorized users can take over the screen,
keyboard and mouse.
* Avoid running X applications with output to a remote display.
Otherwise, X magic cookie information can be captured from the
network while X clients connect to the remote display, so that
unauthorized users can take over the screen, keyboard and mouse.
Finally, steps that can help to keep the current SATAN password
secret:
* Avoid sharing the SATAN directories with other hosts. Otherwise,
SATAN password information may be captured from the network while
the HTML software accesses passworded files, so that unauthorized
users can take over the SATAN HTML server.
* Avoid running SATAN with output to a remote display. Otherwise,
SATAN password information can be captured from the network while
URL information is shown on the remote display, so that
unauthorized users can take over the SATAN HTML server.
ADDITIONAL SATAN DEFENSES
The SATAN software spends a lot of effort to protect your computer
and data against password disclosure. With version 1.1 and later,
SATAN even attempts to protect you after the password has fallen
into the hands of unauthorized users:
* SATAN displays a warning and advises the user to not contact
other HTML servers from within a SATAN session, when it finds
that the HTML client program reveals SATAN password information
as part of parent URL information.
* SATAN rejects requests that appear to come from hosts other than
the one it is running on, that refer to resources outside its own
HTML tree, or that contain unexpected data.
* SATAN terminates with a warning when it finds a valid SATAN
password in an illegal request: SATAN assumes the password has
fallen into the hands of unauthorized users and assumes the
worst.
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The CERT Coordination Center staff thanks Wietse Venema for his cooperation
and assistance with this revised advisory.
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If you believe that your system has been compromised, contact the CERT
Coordination Center or your representative in the Forum of Incident
Response and Security Teams (FIRST).
If you wish to send sensitive incident or vulnerability information to
CERT staff by electronic mail, we strongly advise that the e-mail be
encrypted. The CERT Coordination Center can support a shared DES key, PGP
(public key available via anonymous FTP on info.cert.org), or PEM (contact
CERT staff for details).
Internet E-mail: cert@cert.org
Telephone: +1 412-268-7090 (24-hour hotline)
CERT personnel answer 8:30 a.m.-5:00 p.m. EST(GMT-5)/EDT(GMT-4),
and are on call for emergencies during other hours.
Fax: +1 412-268-6989
Postal address: CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh, PA 15213-3890
USA
CERT advisories and bulletins are posted on the USENET newsgroup
comp.security.announce. If you would like to have future advisories and
bulletins mailed to you or to a mail exploder at your site, please send mail
to cert-advisory-request@cert.org.
Past advisories, CERT bulletins, information about FIRST representatives, and
other information related to computer security are available for anonymous
FTP from info.cert.org.
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Copyright 1995 Carnegie Mellon University. Conditions for use, disclaimers,
and sponsorship information can be found in
http://www.cert.org/legal_stuff.html and ftp://ftp.cert.org/pub/legal_stuff .
If you do not have FTP or web access, send mail to cert@cert.org with
"copyright" in the subject line.
CERT is registered in the U.S. Patent and Trademark Office.
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Revision history
Sep. 23, 1997 Update copyright statement
Aug. 30, 1996 - Information previously in the CA-95:07 and CA-95:07a README
files was inserted into the advisory.
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